This invention relates, in general, to methods and apparatus for the rapid and semi-automated assay of materials indicative of the presence of microbial species such as bacteria.
The ability to rapidly and conveniently detect microorganisms is important for several industries, such as food preparation, medicine, beverages, toiletries, and pharmaceuticals. For example, the ability to detect bacterial contamination, particularly on surfaces, is paramount to improving safety in food processing and food service industries. During food processing, food can become contaminated with bacteria and then spoil. Furthermore, such contamination can be spread through contact of food with contaminated surfaces. Food poisoning can result if food contaminated with pathogenic bacteria, or its toxic products, is ingested without proper cooking. Public awareness of this potential problem is reflected in articles appearing regularly in the popular press. See, for example, Brody, J., xe2x80x9cA World of Food Choices, and a World of Infectious Organisms,xe2x80x9d and xe2x80x9cClean Cutting Boards Are Not Enough: New Lessons in Food Safety,xe2x80x9d The New York Times, Jan. 30, 2001. In addition, spread of disease in hospitals and other facilities often occurs as a result of the passage of infectious microbes on the surface of clothes or equipment.
In light of this potential hazard, it is not enough to simply clean or sanitize a surface and assume it is free from microorganisms such as bacteria. Instead, there is a critical need to perform a test to detect whether the surface is actually free of microorganisms. Thus, random areas of a surface, such as a food preparation surface, can be tested for microorganisms to determine the general cleanliness of the surface.
One of the oldest methods to check for cleanliness involves culturing samples for bacteria. A test surface is chosen and wiped with a swab, and then the swab is smeared onto a culture medium. The medium is incubated and then checked for the presence of bacterial colonies grown in the medium. This is essentially the same type of procedure that is followed in the health services area when testing biological samples, such as a throat swab, for the presence of bacterial species such as streptococcus. Over the years, various types of culture media have been developed, along with numerous products based thereon. While the results of bacterial cultures are accurate, they are limited by the time that it takes to incubate the culture, usually on the order of days.
Unfortunately, such prior art methods for detecting bacterial contamination are too cumbersome and time consuming for immediate use by untrained workers. In particular, much more rapid bacterial assays are needed, particularly in slaughterhouses and food handling establishments. In these locations one must rapidly determine whether additional cleaning methods are required or whether proper safety procedures have been followed. Bacterial assays would be a useful component of a xe2x80x9chazards and critical control points programxe2x80x9d (HCCP) to monitor and control bacterial contamination. However, typical bacterial assays based on cell culture techniques cannot provide results within a meaningful time frame.
In response for a need to obtain results more quickly, other methods for detecting microorganisms have been developed. The most productive area of development has focused on the detection of biomass on the test surface. Biomass includes living cells, dead cells, and other biotic products such as blood, and food residue. Biomass can be detected by an assay for ATP, adenosine triphosphate, a chemical found in all living organisms.
This assay is generally based on the xe2x80x9cfireflyxe2x80x9d biochemical reaction that produces the characteristic bioluminescence associated with fireflies. The specific chemistry of this reaction will be discussed in more detail below. When appropriate reagents are mixed with a sample taken from a test surface, extracellular ATP immediately reacts and generates detectable chemiluminescence. However, intracellular ATP cannot be detected unless the ATP is first extracted from within the cells. Typically, this is accomplished by mixing the sample with an extraction reagent (releasing reagent) that extracts the ATP from within the cells or lyses the cells to permit access of ATP to chemiluminescent reagents. Typical extraction reagents are detergents. The extracted ATP then can be mixed with the luciferase/luciferin reagent to produce the observable reaction. It is important that the extraction reagent chosen does not inactivate the reagents. An additional consideration is the toxicity of the lysing agent, particularly when used on food preparation surfaces.
Chemiluminescent assays of ATP have traditionally been conducted using two basic types of systems: vial systems and all-in-one swab devices. A vial system uses a series of vials containing the reagents necessary to conduct the ATP tests. An all-in-one swab device provides all of the reagents and the swab in a self-contained apparatus.
In a vial system, for example, a first vial contains the extraction reagent, a second vial contains dried reagents, and a third vial contains a buffered solution. At the time of the test, addition of an appropriately buffered solvent from the third vial to the vial containing the reagents results in the re-hydration of the reagents.
Wiping a xe2x80x9cQ-Tip(copyright)xe2x80x9d type swab across the testing surface effectively samples whatever organisms may be present. Usually, the swab is pre-wetted with saline or an appropriate buffer solution. The swab containing the sample is placed in a test tube. Next, the proper amount of extraction reagent from the first vial is pipetted into the test tube containing the swab. After sufficient time has passed to ensure ATP extraction, the buffered solution containing hydrated reagent is pipetted into the test tube and the chemiluminescent reagents are allowed to react with the ATP. The test tube is then placed into a luminometer where the amount of light produced by the reaction is measured. If more than one sample is taken, each sample is placed in its own test tube.
Although vial systems can produce acceptable results, there are deficiencies. One significant problem is that the reagent solutions must be used within a short time of their preparation. If leftover solution is saved for later tests, the reagents will likely degrade and ultimately become ineffective, thus producing no reaction even in the presence of ATP (a false negative result). This problem is compounded by commercial producers of typical reagents that sell the reagent only in quantities that produce an amount of solution that is greater than that needed for individual tests. Furthermore, the alternative, dried reagents, can be relatively costly. Thus, the vial system results in waste of expensive reagents when only an individual test is required. Another shortcoming of vial systems is that accurate pipetting and mixing of reagents is required. A pipette is used to transfer the reagents from vial to vial or vial to tube. While pipetting can be highly accurate, it is laborious and time consuming. Also, if any of the vials or pipettes are not sterile, the biomass contained in them will produce a false positive for the presence of ATP. Furthermore, proper pipetting technique requires significant skill and experience, thus making consistent and accurate results difficult to attain without a relatively high degree of expertise on the part of the operator.
The all-in-one swab devices apply the same reaction as the vial systems but keep all of the reagents and swab in a self-contained apparatus that fits into a luminometer or, alternatively, can create a test solution that can be transferred (and transported) to a standard cell for a luminometer. More specifically, the all-in-one devices typically involve a swab that is placed in a plastic tube containing several chambers. An advantage to this system is that a unit dose of each reagent is provided for one test, thus avoiding waste of reagents when only one test is required. However, a certain procedure must be followed using an all-in-one device to ensure that the reagents are combined at the appropriate times and in the appropriate sequence.
In a typical all-in-one device, a swab pre-wetted with a wetting solution is placed in a sealed tube until ready for use. The wetting solution may contain an extractant. The sealed tube prevents evaporation of the wetting solution. At the appropriate time, the device is opened, the operator removes a pre-wetted swab, and collects a sample by wiping the swab along the testing surface. If present, the extractant will result in the release of intracellular ATP from the sample collected on the swab. The operator then places the swab back in the tube and the tube, once resealed, is ready for the ATP present in the sample to react with the chemiluminescence reagents.
Although numerous technologies have evolved in the implementation of all-in-one ATP assay systems, devices available to date have consistently displayed shortcomings rendering them less than ideal for use under the conditions most likely to be encountered. Examples in the prior art illustrate how others, with less than complete success, have approached the various problems discussed herein. For example, European Patent Application No. 0 309 429, entitled xe2x80x9cLuminometric assay of cellular ATP,xe2x80x9d to Life Sciences International AB, discloses methods and an apparatus directed toward quantitation of biomass in a sample specimen. The disclosed apparatus comprises a reagent carrier and a fibrous sampling element (either separate or combined in a single structure), along with cuvettes containing a buffering solution into which the sampling element is placed for luminometric analysis. Due to the stated purpose of the device to obtain results for total bacterial biomass, the disclosed method comprises treatment of an aliquot of a liquid sample at elevated temperatures for a time sufficient to evaporate essentially all of the solvent medium for the purpose of degrading non-bacterial ATP from the sample. Also included in the apparatus and method is a calibration stick containing a known amount of ATP standard in a dried form. However, the disclosed apparatus and methods still suffer from considerable complexity and limited application, as the actual luminometric measurements giving rise to a biomass determination are contemplated to be performed on a laboratory-scale apparatus. Thus, the complexity of the process and the need for a full-scale laboratory apparatus imposes a requirement for operator skill and sophisticated equipment that renders the disclosed invention unsuitable for rapid, in situ analyses by untrained personnel in less-than-ideal field conditions.
PCT application WO 95/25948, entitled xe2x80x9cSample Collecting and Assay Device,xe2x80x9d to Celsis International PLC, discloses a hand-held sampling device comprising a glass tube with one or more reagent wells sealed by a frangible membrane or foil, as well as a sampling swab made from a suitably absorbent material. The disclosed use for the sampling device contemplates piercing one of the frangible seals with the sampling swab to moisten the swab, sampling a surface to be analyzed with the moistened swab, returning the swab with sample to the device and further puncturing the remaining one or more frangible seals to expose the swab with sample to reagent solutions contained therein. The sampling device, wherein the swab has been exposed to reagent solutions, can then be placed, after a suitable period of incubation, in a luminometer to measure the level of chemiluminescence from the sample, although the reference fails to disclose details of the type or construction of the luminometer. Alternatively, the sampling device may comprise a single reservoir with a frangible seal, wherein the reservoir contains a wetting solution only. It is clear that the disclosure is directed solely toward the sampling device only and contemplates measurement of chemiluminescence collected with the device of the invention in a conventional, laboratory-scale instrument, specifically adapted to hold the sampling device or to receive sample-containing solutions from the device. Thus, the disclosed invention, due to the relative complexity of the multi-compartment sampling device using reagents in solution form, along with the need for a relatively sophisticated measurement instrument is not ideally suited for use by untrained operators in the relatively harsh conditions of a field environment.
PCT application WO 98/27196, entitled xe2x80x9cSample-Collecting and Assay Device,xe2x80x9d to Celsis International plc, discloses a hand held sampling device with a pen-type configuration. The sampling device comprises a fluid reservoir with a frangible seal, which seal may be broken by the inward depression of a top portion of the device, releasing wetting solution that travels downward through an internal portion of the device, wetting a conventional absorbent swab. The swab may then be removed to sample a surface and returned to the device. Thereafter, a bottom cuvette portion is pressed upward breaking a frangible seal between the swab-containing central portion of the device and the bottom cuvette portion and releasing fluid from the central portion into the cuvette portion. The cuvette portion may contain further reagents in dried form. A window in the cuvette wall permits visual inspection of a color developed by a reaction between sample and reagents. Alternatively, light may be emitted from the sample by ATP-chemiluminescence. However, as with WO 95/25948, the application does not disclose details of the luminescence measuring device, although the implication is clear that the device would be a laboratory-scale instrument, perhaps adapted to receive the disclosed sampling device.
U.S. Pat. Nos. 5,827,675 and 5,965,453, both entitled xe2x80x9cTest Apparatus, System and Method for the Detection of Test Samples,xe2x80x9d Skiffington and Zomer, inventors, and assigned to Charm Sciences, Inc., disclose a multi-component sampling device designed to be used with a desktop analytical luminometer. The sampling device is comprised of a cover portion into which is removably secured a xe2x80x9cQ-Tip(copyright)xe2x80x9d style swabbing stick with an absorbent material on one end. In operation, the cover and swab are removed from the central portion of the sampling device and the tip of the swab, presumably after being wetted with an external solution, is rubbed across a surface to be analyzed. The swab is then returned to the sampling device where the portion of the device containing the swab is moved downwardly within the device, rupturing frangible seals between sequential reagent-containing reservoirs. Continued downward movement results in the swab tip being immersed in the reagent solutions released from the storage reservoirs in a microtube test unit that forms the bottom component of the sampling device. This test unit may also contain a reagent tablet that, upon contact with the solutions from the ruptured storage reservoirs releases reagents necessary to generate the analytical signal. The microtube test unit is then removed from the sampling device, sealed with an aluminum seal stored on the external surface of the device and transported to the desktop analytical instrument where either color or a luminescent signal is recorded. Although offering a number of advantages over prior art methods and devices, the invention disclosed in this reference still suffers from the drawbacks of a somewhat complex internal structure to the sampling device, and the extensive handling required to remove the microtube from the bottom of the device and seal the same before being transported to a separate desktop analytical device for actual measurement.
In a series of applications (see EP 0 717 840 B1; EP 0 439 525 B; WO 95/07457; and WO 90/04775), Biotrace Ltd. has disclosed, generally, a test kit comprising a luminometer and a sampling device for determination of bacteria and other living cells for an assessment of hygienity. The kit comprises a luminometer with a photodetector, wherein the detector is an avalanche photodiode; a plurality of pipettes and pipette tips, sample vessels, sterile swabs, and containers of reagents for fluorescence or luminescence reactions. The cuvettes may also contain appropriate enzymes in a dried form for the chemiluminescent or fluorescent reactions. In operation, a sterile swab is removed from its packaging, wiped across a surface to be analyzed, and returned to a pipette tip. The pipette tip is then attached to a pipette, and the pipette is used to draw a predetermined exact volume of appropriate reagent solution, such as a solution containing a lysing agent, into the pipette. The resultant mixture is allowed to incubate for a suitable period of time. The reagent within the pipette is then transferred to a cuvette, where the solution is withdrawn back into the pipette and then re-transferred to the cuvette a number of times in order to ensure adequate mixing. The cuvette is then placed in the luminometer where emission is measured. Although the invention disclosed in these applications offers some advantages over other prior art methods and devices, in that the kit of the invention comprises a portable analytical device, the invention as a whole still presents some significant shortcomings. Principal among these is the relative complexity of the process by which a sample swab interacts with the reagents necessary to develop an analytical signal. As one of skill in the relevant art would recognize, there is a considerable amount of skill required in the manipulation of pipettes and other such transfer glassware in order to insure proper preparation of resulting solutions. Thus, the disclosed invention would likely not be ideally suited for use by untrained operators in the harsh and variable conditions found in the field.
U.S. Pat. No. 4,978,504, entitled xe2x80x9cSpecimen Test Unit,xe2x80x9d to Nason, discloses, in general, a sample collection device adapted for applications involving chemiluminescence assays. The disclosed sample collection device comprises a cap portion to which is attached an elongated swab, the distal tip of which comprises a xe2x80x9cQ-Tip(copyright)xe2x80x9d style absorbent material. The cap portion also contains a storage well in which is a frangible glass ampoule within which is stored a suitable reagent, or other, solution. The storage well is separated from the distal swab portion by a porous filter disk. Alternatively, the filter disk may be impregnated with additional reagents. In operation, the cap portion is removed from the device and the swab tip is used to collect sample from a surface to be analyzed. The cap and swab assembly is then returned to the sampling device. The top-most portion of the cap is then squeezed or otherwise deformed so that the reagent-containing ampoule is broken to release its contents to flow downwardly through the device to the swab tip. The filter disk effectively permits the flow of solution without permitting the passage of remnants of the broken ampoule. If the filter disk is impregnated with additional reagents, then these presumably mix with the fluid contents of the ampoule as that fluid flows downwardly through the device. The solution/reagent mix flows over the swab tip and collects in the bottom portion of the sampling device. At this point, the sampling device may be inserted into an analytical instrument for a determination of the luminescence from the sample, but the reference does not disclose details on the type or construction of such a device. Presumably, such an instrument would be a laboratory-scale device. Alternatively, the sampling device can be used to transport the sample/reagent to a cuvette or other sample cell for analysis in a conventional instrument. As with other examples of the prior art, this reference exhibits shortcomings in overall design that render it incapable of meeting the ideal criteria for such a device articulated herein. For example, the device is somewhat complex in design and manufacture and requires the use of glass ampoules as reagent reservoirs. Given the likely storage and use of such a sampling device in the field, such constructions are less than ideal.
U.S. Pat. No. 4,672,039, entitled xe2x80x9cApparatus for Registering the Presence of Bacteria, Particularly in Field Conditions,xe2x80x9d Lundbloom, inventor, and assigned to AB Sangtec Medical, discloses a portable field-test apparatus for the detection of a threshold level of bacteria in samples. The device is designed to receive an injection of a liquid sample suspected of harboring bacterial organisms onto a filter portion of the device. The bacteria so introduced to the device then have a series of reagent solutions sequentially sprayed upon them, the solutions comprising sodium hydroxide, luminol and perborate in precise amounts. An opening in the device is then closed and a transparent window portion permits chemiluminescence from the sample to impinge upon a light recording means that is preferably a piece of photographic, Polaroid-type, film. Although the disclosed device is presumably capable of use under field conditions, the complex process of the sequential spraying of specific amounts of different reagents, the need to utilize a liquid sample and the requirement for a light-tight environment imposed by a photographic film detector all represent significant departures from an ideal configuration or method of use.
U.S. Pat. No. 4,353,868, entitled xe2x80x9cSpecimen Collecting Device,xe2x80x9d Joslin and Dennison, inventors, assigned to Sherwood Medical Industries, Inc., discloses, generally, a sampling device. The disclosed invention comprises a multi-part sampling device with a top cap portion to which is attached a xe2x80x9cQ-Tip(copyright)xe2x80x9d style swabbing stick with an absorbent material on one end, and a container portion that houses a solution reservoir. The solution reservoir is separated from the upper body of the container portion by a frangible seal. In use, the upper cap portion is removed and the exposed swab tip is used to swipe a surface suspected of bacterial contamination. The cap portion is then returned to the device wherein a downwardly directed force ruptures the membrane covering the solution reservoir and immerses the swab tip into the solution contained therein. The sample exposed to the reagent solution within the device may then be transported to a laboratory environment where the solution may be subsequently transferred to an appropriate sample cell or cuvette for analysis in a laboratory-scale instrument. However, the relatively short time over which emission of measurable luminescence will occur from the sample is such that the time between the rupture of the reservoir seal to transfer of the resulting solution to an analytical instrument must be rather short. It is clear from the disclosure of this reference that the invention is suited solely for collection and transport of samples to an analytical facility with the capability for accurate fluorescence measurements. Thus, although the sampling device may be used in the field, there must necessarily be a substantial passage of time from collection of a sample in the field to receipt of actual analytical results.
U.S. Pat. No. 5,624,810, entitled xe2x80x9cMethod for the Detection of Surfaces Contaminants,xe2x80x9d Miller and Loomis, inventors, and assigned to New Horizons Diagnostics Corp., discloses a sample collection device for use in a method to detect the presence of bacteria in a sample. The reference discloses that sample collection can be by means of a xe2x80x9cQ-Tip(copyright))xe2x80x9d style swabbing tip or, alternatively, by means of small absorbent sponges. In practice, the swabbing tip or sponge is wet with a wetting solution and contacted with a surface suspected of bacterial contamination. The swabbing device or sponge is then transferred to a reservoir of collection fluid wherein the sampling material is intimately mixed with the fluid. In the case of the use of sponges for sample collection, the reservoir of collection fluid is physically manipulated to facilitate the mixing of sample with the collection fluid. For a flexible plastic reservoir as disclosed in the reference, the physical manipulation comprises repeated squeezing or wringing out of the sponge within the reservoir. The disclosed method contemplates the use of a large volume concentration apparatus into which is delivered the extraction fluid from the external reservoir after mixing with the sampling device. The bacterial cells in the concentrated sample are then lysed and the resultant mixed with appropriate chemiluminescence reagents. A volume of the ATP-containing fluid is then transferred to an appropriate instrument for measurement of emission intensity. It would be apparent to one of skill in the relevant art that such an apparatus and method involves considerably more complexity than would be suitable for use under field conditions by an unskilled operator. Thus, the teachings of the reference fall far short of attaining the goals of an ideal apparatus or method for hygiene monitoring.
In U.S. Pat. No. 5,783,399, entitled xe2x80x9cChemiluminescent Assay Methods and Devices for Detecting target analytes, Childs et al., inventors, and PCT application WO 08/49544, entitled xe2x80x9cHand-Held Luminometer,xe2x80x9d McClintock et al., inventors, both assigned to Universal Healthwatch, Inc., there are disclosed a sampling and luminescence developing device, and a hand-held luminometer in which to read the luminescence signal so generated. The references disclose a sample collection and signal development device comprising an absorbent material, such a filter paper, for collection of samples and a second absorbent material for loading with appropriate reagents for the generation of a chemiluminescence signal. Alternatively, the device may combine the sample collection and reagent storage portions in a single structure of absorbent material. The device may also contain a reservoir of carrier liquid. Upon collection of a sample by wiping the absorbent material on the surface to be analyzed, a carrier fluid is applied from the reservoir to the absorbent material and, by wicking action, travels horizontally along the thin strips of absorbent material. The movement of the carrier fluid by capillary action through the absorbent material results in the migration of sample and/or reagent to a reaction zone wherein a chemiluminescent reaction may take place. The emission generated by such reaction is released from the device through a form of transparent window and subsequently impinges upon the detector portion of a luminometer. The luminometer disclosed by the references comprises a handle portion and a head portion, the head portion further comprising one or more electronic components of the device, such as a display. The device also comprises a sample section designed to receive the sampling and luminescence development device described immediately above. Alternatively, the sample section may work with a cuvette inserted into the section, the cuvette containing a fluid sample for analysis. The means included in the device for detection of a luminescence signal may comprise a photomultiplier tube, a charge coupled device (CCD), or a photon counting device. The preferred signal detection means is a photomultiplier tube (PMT), such as a Mamamatsu H5773. Although the disclosed devices offer a number of improvements over the prior art sampling and detection devices, the use of the sampling device remains somewhat complex in the requirement for application of a carrier fluid to the sampling device in order to effect contact of the sample with the necessary chemiluminescent reagents. One of skill in the art would appreciate the variations potentially introduced through the need to handle and deliver the carrier fluid.
In a first embodiment, the present invention provides a method for assaying for the presence of an analyte of interest, the method comprising the steps of (a) loading a sampling swab with a first reagent solution comprising a reagent and a solvent; (b) contacting a substance to be analyzed with the swab so as to obtain a sample of at least a portion of the analyte of interest, if any, present in the substance; (c) transferring the sample from the sampling swab to a receptacle; (d) contacting the sample with a reactant mixture in the receptacle to induce a chemiluminescent reaction; and (e) measuring the emission of chemiluminescent radiation from the reaction to indicate the presence or absence of the analyte of interest in the sample. Preferably, the analyte of interest comprises cellular material. In one aspect, the method of the present invention contemplates transferring the sample to the receptacle by contacting the sampling swab with a second reagent solution so as to rinse the sample from the swab and into the receptacle. Preferably, the first reagent solution comprises a detergent. More preferably, the detergent is benzalkonium chloride.
In another aspect, the method of the present invention contemplates the use of a first reagent solution comprising a sterile saline solution. Preferably, the first reagent solution is loaded into the sampling swab by contacting the swab with the solution so that the swab absorbs a volume of the solution corresponding to no more than 50% to 80% of a saturation loading for the swab. Alternatively, the first reagent solution is loaded into the sampling swab by contacting the swab with the solution and then evaporating the solvent from the solution. Preferably, the analyte of interest is present in a liquid substance. Alternatively, the analyte of interest is present on a solid surface.
In another aspect, the method of the present invention provides for a receptacle that contains a culture medium suitable for promoting microbial cell growth. In yet another aspect, the reactant mixture comprises a luciferase/luciferin system. Preferably, herein the reactant mixture comprises a firefly luciferase system. Alternatively, the reactant mixture comprises a recombinant luciferase system
In another embodiment, the method of the present invention includes the additional step of filtering the liquid substance through a filter medium effective to remove microbial species from the substance to create a microbial filtrate on the filter medium before contacting the reagent swab with the microbial filtrate.
In yet another embodiment, the method of the present invention contemplates a reactant mixture comprising reagents that break down all nucleic acids present in the sample to inorganic phosphates and convert the inorganic phosphates to adenosine triphosphate (ATP).
In still another embodiment, the method encompasses an analyte of interest comprises a species that can be oxidized by the action of an enzyme to yield an oxidized form of the species and hydrogen peroxide. Preferably, the analyte of interest is selected from the group consisting of sugars, lipids, alcohols, amino acids, amines, and the reduced form of nicotine adenide dinucleotide (NADH). In one aspect, this embodiment of the invention provides for a reactant mixture comprising an enzyme capable of oxidizing the analyte of interest to an oxidized form and hydrogen peroxide, and reagents capable of reacting with hydrogen peroxide to produce a chemiluminescence emission.
In still another embodiment, the receptacle used in the practice of the method of the present invention contains an immunospecific species capable of binding to the analyte of interest. Preferably, the immunospecific species is bound to a solid surface within the receptacle. More preferably, the immunospecific species is bound to microspheres. In a specific aspect of the practice of the method of the present invention, the method comprises the additional step of removing all species present in the receptacle that are not bound to the immunospecific species before contacting the sample with a reactant mixture. Preferably, the immunospecific species is an antibody to the analyte of interest or an antigen to the analyte of interest. Alternatively, the analyte of interest is an antibody.